Calculate the electrochemical equilibrium potential ie Nerns

Calculate the electrochemical equilibrium potential (i.e., Nernst potential or E_ion) for each ion for the mammalian neuron. For a range of ionic concentrations, select the highest concentration. It is only necessary to show the work for one calculation (i.e., set up the equation).

Given the resting membrane potential (E_m) of -83.9 mV, identify in which direction (i.e., OUT of or IN to the cell) each ion will move if the membrane were permeable to that ion.

Which ion is most likely dominating the membrane potential in 2 above? Why?

Rank the driving forces for each ion from strongest to weakest.

TABLE 2.1 Extracellular and Intracellular lon Concentrations CONCENTRATION (MM) ION INTRACELLULAR EXTRACELLULAR Squid neuron Potassium (K+) 400 20 440 50 Sodium (Na 560 Chloride (Cl 40-150 0.0001 10 Calcium (Ca2+) Mammalian neuron Potassium (K 140 145 Sodium (Na 5-15 4-30 110 Chloride (Cl) 0.0001 1-2 Calcium (Ca2+ NEUROSCIENCE 5e, Table 2.1 O 2012 Sinauer Associates, Inc.

Solution

the nernst potential equation for calculating the equilibrium potential is as follows:

Veq = RT/zF ln [Xo]/[Xi]

where R is the gas constant, T is temperature, z is the valency, F is faraday\'s constant, Xo is the extracellular concentration of ion and Xi is intracellular concentration.

if we setup this equation for an ion, say sodium , it would be

Veq = 8.314 x 273/1 x 96485 ln 145/15

which is approximately equal to +60.60 mV

since the resting membrane potential is -83.9 the sodium ion would move in the cell.

the most dominating ion is the membrane potential should be calcium because it has the highest extracellular concentration with respect to its intracellular concentration.

the strongest driving force would be of calcium and the weakest would be pottasium as it has the least extracellular concentration related to intacellular concentration.